1. Field of the Invention
The present invention generally relates to a lockup device of a hydraulic torque transmission device. More specifically, the present invention relates to a lockup device having a multi-face clutch, in which a piston presses a friction plate to a friction surface of a front cover.
2. Background Information
A torque converter is a device for transmitting a torque of an engine to a transmission side via an internal working fluid, and primarily includes a front cover receiving torque from an engine, an impeller fixed to a transmission-side portion of a front cover to form a fluid chamber, a turbine opposed to an engine-side portion of the impeller for providing torque to a transmission side, and a stator arranged between radially inner portions of the impeller and the turbine for rectifying the working fluid flowing from the turbine toward the impeller.
The lockup device is a device arranged in a space between the turbine and the front cover for mechanically coupling the front cover and the turbine together, and thereby directly transmitting the torque from the front cover to the turbine. The lockup device includes a disk-like piston, which can be pressed to a friction surface of the front cover for coupling, and an elastic coupling mechanism for transmitting the torque between the piston and the turbine.
A lockup device which includes two friction surfaces for increasing a torque transmission capacity has already been proposed. For example, this lockup device includes a clutch mechanism having a frictional coupling portion opposed to a friction surface of a front cover, a piston for pressing the frictional coupling portion to the front cover, and an elastic coupling mechanism elastically coupling the turbine and the clutch mechanism fixed to the turbine together in the rotating direction (e.g., see Japanese Laid-Open Patent Publication No. H9-112651).
More specifically, the clutch mechanism includes a friction plate having a frictional coupling portion adjacent to the friction surface of the front cover, and a piston which has a pressing portion adjacent to the frictional coupling portion, and can be axially moved by a hydraulic pressure. The piston is coupled to the front cover via return plates formed of plate springs. Owing to this coupling, the piston rotates together with the front cover, and is moved away the front cover by an elastic force of the return plates when the clutch is released. The elastic coupling mechanism includes a plurality of springs each having circumferential ends supported by the friction plate, and a driven plate supporting the circumferential ends of the springs fixed to the turbine.
The prior art, in which the mechanism coupling the front cover to the piston is formed with return springs that are made of plate springs, requires members such as rivets or bolts for fixing the opposite ends of each return spring. This increase the number of required parts, and complicates the structure so that the weight of the structure increases. Furthermore, the number of manufacturing steps increases.
In addition, the piston coupling mechanism is arranged in a radially middle portion of an axial space between the front cover and the turbine. Therefore, sufficient space cannot be ensured for the spring members of the damper mechanism. Consequently, it is impossible to increase the sizes of the spring members, and thus impossible to increase the vibration absorbing properties without difficulty.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved lockup device having a piston for pressing a frictional coupling portion of a friction plate to a front cover, and particularly to simplify a mechanism for coupling the piston to the front cover. In addition, it is also apparent to those skilled in the art that there exists a need for an improved lockup device having a piston for pressing a frictional coupling portion of a friction plate to a front cover, and particularly to ensure a space for a spring member of a damper mechanism. This invention addresses these needs in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.